Pollution control devices are used to reduce atmospheric pollution from the exhaust systems of internal combustion engines such as, for example, those used in motor vehicles (e.g., automobiles, watercraft, aircraft, etc.), power generators and the like. Two typical types of such pollution control devices are catalytic converters and exhaust system filters (e.g., diesel particulate filters) or traps. Catalytic converters contain one or more catalyst support elements, which are typically monolithic structures coated with desired catalyst material. The monolithic structure is typically made of ceramic, although metals have also been used. The catalyst(s) oxidize carbon monoxide and hydrocarbons or reduce the oxides of nitrogen in exhaust gases. Exhaust system filters typically include a filter element in the form of a honeycombed monolithic structure made from porous crystalline ceramic materials. In the current state-of-the-art construction of these pollution control devices, their monolithic structure is mounted within a metal housing.
Protective packing or mounting materials are typically positioned between the pollution control element (e.g., monolithic structure) and the metal housing to protect the pollution control element, for example, from road shock and vibration and to prevent exhaust gases from passing between the pollution control element and the metal housing. When a ceramic monolithic structure is used, such mounting materials typically need to compensate for the thermal expansion difference between the metal housing and the ceramic monolith. The process of mounting such a monolithic structure in a housing, with a mounting material, is referred to as “canning”. Such mounting processes have included inserting the monolith into the housing and injecting a paste into the gap between the monolith and the metal housing. Other mounting processes have also included wrapping a sheet material or mat around the monolith and inserting the wrapped monolith into the housing and welding the housing closed. The compositions used to form conventional mounting materials have included a variety of non-intumescent materials and intumescent materials.
The present invention is an improvement over such prior pollution control element mounting systems.